title: Fluorescence solvatochromism in lumichrome and excited-state tautomerization: a combined experimental and DFT study.
abstract: Fluorescence solvatochromism of lumichrome (LC) was studied by steady-state and time-resolved fluorescence spectroscopy. The excited-state properties of LC do not show any correlation with solvent polarity, however, reasonably good correlation with solvent E(T)(30) parameter was observed. A quantitative estimation of contribution from different solvatochromic parameters, like solvent polarizability (π*), hydrogen bond donor (α), and hydrogen bond acceptor (β) ability of the solvent, was made using linear free energy relationship on the basis of Kamlet-Taft equation. The analysis reveals that hydrogen bond donating ability (acidity) of the solvent is the most important parameter that characterizes the excited-state behavior of lumichrome. Quantum mechanical calculations using density functional theory (DFT) were done to study the most stable structure and excited-state tautomerization process of LC toward the formation of isoalloxazines. Charge localization in the excited state and formation of hydrogen-bonded cluster through solvent hydrogen bond donation on the N10 atom of alloxazine moiety were predicted to be the key step toward this water-catalyzed tautomerization process.
authors.affiliation: Department of Chemistry, North-Eastern Hill University, Shillong, India.
authors.forename: N Shaemningwar
authors.initials: NS
authors.lastname: Moyon
authors.forename: Sivaprasad
authors.initials: S
authors.lastname: Mitra
mesh_terms: D003116:Color; D005415:Flavins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D005415:Flavins; D012997:Solvents; C001559:7,8-dimethylalloxazine